


Bitches Get Switches

by CaitieLewd



Category: Undertale (Video Game)
Genre: Aftercare, BDSM, Bondage, Consensual bondage, Cunnilingus, Degradation, Dirty Talk, Discipline, Dom Sans, Dom/sub, Dry Humping, Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Face-Sitting, Fontcest, Forced Chastity, Frottage, Gags, Hand Jobs, High Heels, Humiliation, I am so proud of this title you have no idea, Lingerie, M/M, Mating Cycles/In Heat, Multiple Orgasms, Oral Sex, Orgasm Delay/Denial, Orgasm Denial, Overstimulation, Punishment, Riding Crops, Sub Papyrus, Swapfell, more tags to come
Language: English
Status: Completed
Published: 2017-10-02
Updated: 2017-10-05
Packaged: 2018-12-24 21:21:16
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 7,313
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12021234
Author URL: https://archiveofourown.org/users/CaitieLewd/pseuds/CaitieLewd
Summary: In the Swapfell AU, Slim is beginning his heat cycle, and it’s been driving Black crazy all day. The moment they get home, Slim gets exactly what is coming to him.





	1. Bitch in Heat

**Author's Note:**

> Welcome to day 2 of Kinktober! Today's prompts were dirty talk, watersports, and forniphilia (human furniture). I went with dirty talk! In case you're wondering, yes on some of them I did choose more than one of the kink prompts. But only if it really fit the concept that came to mind (or if I REALLY liked the kink).
> 
> I don't know how canon these nicknames are for this AU, but for the sake of clarity I always refer to AU variant Sans and Papyruses as their most commonly used nicknames, even if no other AUs are involved in that particular story. Swapfell Sans is Black, and Papyrus is Slim.

Black audibly ground his teeth together as he approached the front of their house. Slim winced at the sound, keeping his head meekly bowed and steps silent as he trudged along behind the other skeleton. He was in trouble, and he knew exactly why.

Black muttered under his breath as he fumbled with the keys, nearly dropping them twice before finally unlocking the door. As soon as Slim had shut the door behind them, Black grabbed him by his collar and yanked him down to his eye level.

“BROTHER. I AM UPSET WITH YOU. DO YOU KNOW WHAT FOR?”

“y-yes, m’lord,” Slim stammered, an orange glow creeping onto his face, to match the glow in his distractingly tented trousers.

“OH, _GOOD_ , THEN I WON’T HAVE TO EXPLAIN HOW MUCH I HATE IT WHEN YOU GO INTO HEAT IN PUBLIC?!”

“no, m’lord. i’m sorry, m’lord.”

“IF YOU ARE SORRY, THEN TELL ME WHY YOU ALLOWED THAT TO HAPPEN, MUTT.”

Slim swallowed, sweat beading on his forehead. “b-because...m’lord...you…”

Black’s grip on the collar tightened and he yanked his brother down another, painful inch. “I _WHAT?_ DO YOU MEAN TO IMPLY THIS IS SOMEHOW _MY_ FAULT?!”

Slim flinched, but obediently refrained from pulling away. “n-n-no! no i-it’s not your fault, m’lord, it’s just that…yo-your outfit, i-it...”

Black’s glittering stiletto boots tapped on the floor. “I’M WAITING, MUTT.”

“you...you just look s-so _hot,_ m’lord!” Slim confessed.

“YOU’RE DAMN RIGHT I DO, MUTT. I DIDN’T GO TO TOWN TO BUY UGLY BATTLE ARMOR.” Black used his free hand to toss a glossy, mauve scarf over his shoulder. “BUT DOES THAT GIVE YOU PERMISSION TO GO INTO HEAT WHILE WE’RE ON A SIMPLE OUTING?”

“n-no, m’lord! not at all!”

“BUT YOU COULDN’T HELP YOURSELF, COULD YOU?”

“no, m’lord!” Slim panted, squirming in place as his pants rubbed ever so lightly over his aching erection. Perhaps noticing his discomfort, or simply tiring of holding him, Black released the collar. Slim rubbed the back of his neck nervously, but didn’t dare stand up to full height.

“TCH. YOU’RE NO BETTER THAN A DOG IF YOU CAN’T CONTROL WHEN YOU’RE GOING INTO HEAT. ARE YOU A DOG, MUTT?”

Slim bowed his head. “yes, m’lord. i...i’m a dog.”

“NO...NOT JUST A DOG, YOU’RE A _BITCH_ , AREN’T YOU? YOU’RE A BITCH IN HEAT.”

“i’m a bitch in heat, m’lord.”

“LOOK AT ME WHEN YOU SAY IT.”

Slim’s eyes reluctantly met Black’s piercing gaze. “i-i’m a b-bitch in heat…m’lord.”

“AND _WHOSE_ BITCH ARE YOU?”

“yours, m’lord.”

Black nodded approvingly. “THAT’S RIGHT. AND GOOD BITCHES OBEY THEIR OWNERS, DON’T THEY?”

“yes, m’lord.”

A wicked grin grew on Black’s face. The scent of his brother’s heat and the magic his arousal put off was thick in the air, threatening to trigger his own heat. And if they were going to be in heat, he may as well take control of the situation and make the best of it. He grabbed a whip hanging from the nearby coat rack. “SO IF I ASK YOU TO GO TO YOUR ROOM AND NOT TOUCH YOURSELF FOR THE NEXT THREE HOURS WHILE I FINISH MY PATROL, YOU’LL DO IT, RIGHT BITCH?”

Slim let out a small whine, starting to quiver. “y-y-yes, m…lord…”

“GOOD. YOU ARE TO STAY ON THE BED AND LEAVE YOUR CLOTHES ON. IF YOU ARE OBEDIENT, I’LL MAKE YOU A HAPPY LITTLE BITCH, HOW DOES THAT SOUND?”

Slim’s jaw fell open for a moment. “that s-sounds wonderful, m’lord. t-thank you, m’lord!”

Black sneered. “IF YOU FOLLOW MY INSTRUCTIONS, I’LL MAKE YOU CUM UNTIL YOU’RE DRY. I WON’T STOP UNTIL YOU _BEG_ ME TO STOP RIDING YOU, AND EVEN THEN ONLY IF I’VE FUCKED THAT WRETCHED HEAT RIGHT OUT OF YOUR COCK. I’LL MAKE YOU HOWL LIKE THE BITCH YOU ARE, AND POUND YOU SO HARD, YOU WON’T WALK STRAIGHT FOR A WEEK.” Slim’s eyes glazed over, and his tongue started to loll out of his mouth as he took a single, shuddery breath. “BUT, IF YOU DISOBEY…”

**_CRACK_ **

The whip hadn’t touched Slim, but it immediately brought him to stand at attention. “y-yes, m’lord. i understand, m’lord.”


	2. Bitch on a Leash

**Summary for the Chapter:**

> Welcome to Kinktober day 8, and welcome back to Swapfell! Today and tomorrow we’re going to be finishing out this saga. I actually pulled a sneaky and flipped today’s prompts with tomorrow’s. Normally I wouldn’t interrupt the flow of kinktober in such a way, but given the sequence of events it simply had to be done. So enjoy some more Slim teasing with lingerie and frottage! The only prompt I left out was asphyxiation, which BELIEVE me was a tough call.

_Cl-click._

_Cl-click._

_Cl-click._

_Cl-click._

Slim swallowed behind the bit gag in his mouth, SOUL pulsing excitedly as each stilettoed tap of his master’s boots came closer, and closer. His bound hands fretted at his sides as he lay facing the ceiling on his bed, fully clothed and further dressed in soft, black ropes that bound him head to toe. Two cords in particular wrapped tightly around each side of his tented groin, causing the crotch of his pants to brush lightly against his cock with horribly unsatisfying friction.

“STILL COMFORTABLE, BROTHER?”

Black appeared in the doorway. Slim could only see his silhouette from the light of the hall, but he was clearly waiting for a response. He wanted the signal. Slim eagerly clicked his feet together twice, making a loud and distinctive sound.

“GOOD,” Black breathed, shutting the door behind him and locking it with a soft snick, darkening the room considerably.

_Cl-click._

_Cl-click._

_Cl-click._

_Click._

Black stopped at the foot of the bed, hands at his hips. Slim gazed upward, drinking in the radiant image of his master. The smaller skeleton was clad in a fine black leather corset, adorned with spikes and small decorative chains that Slim didn’t doubt were made of real metal. Long black gloves wrapped his arms all the way up to his elbows. His midriff was exposed, but violet panties laced with intricate black designs throughout covered his pelvis. There was a glint between his legs which suggested there was something metal sewn into the crotch. Garter straps attached the panties to a pair of fishnet stockings, and Slim could even see the start of his master’s glittering stiletto boots, which had started this whole mess.

“WELL, BITCH? IS _THIS_ WHAT YOU WANTED?” Black taunted, running a hand down the garter straps to mock his captive viewer.

Slim whined behind the gag, twisting in his bonds to lift his head for a better view. It _was._ His brother looked magnificent, radiating perfect authority and power. The revealing, yet intimidating outfit was a perfect match to Black’s confident dominance, not just over him, but also over anyone else who dared to stand before him.

“I’LL TAKE THAT AS A YES,” Black sneered. In a single, smooth movement he hopped on the bed to stand above Slim, balancing on the mattress in his heels with impossible grace.

“THOUGH YOU WOULD BE WISE TO ANSWER ME WHEN I ASK YOU A QUESTION, BITCH,” Black said darkly. He brandished a riding crop which had previously been hidden from Slim’s view. “YOU’RE LUCKY I’VE GONE TO THIS MUCH TROUBLE FOR SUCH AN UNRULY MONGREL. YOU’VE FOLLOWED MY INSTRUCTIONS SO FAR, BUT YOU REMEMBER WHY WE’RE HERE, CORRECT?”

Slim nodded vigorously. “mmhmph,” he mumbled.

_Whack!_

The crop instantly smacked Slim’s bare foot bones. Slim yelped and jerked back. Black sighed exhasperatedly. “WE’VE COME TOO FAR FOR YOU TO FORGET HOW I AM TO BE ADDRESSED, MUTT.”

“ysh, m’lrd! shhorry, m’lrd!” Slim spluttered, his red-orange tongue dancing behind the bit as it barely managed to form distinguishable sounds.

“THAT’S BETTER.” Black stepped closer to his prey, until he stood straddled over Slim’s bound legs. Slim held himself perfectly still, fighting the urge to squirm with nervous excitement and urgent arousal. He knew any unnecessary movement would knock his brother off balance, and that would not end well for either of them.

At that tangle, Slim also couldn’t help but notice that there were, in fact, rows of pointed metal studs embedded in the crotch of his master’s panties. He swallowed, taking that as a sign of what was coming.

“AS I WAS SAYING, YOU’VE DONE AS I HAVE ASKED SO FAR, BITCH. YOU STAYED IN HERE FOR THREE WHOLE HOURS ALL BY YOURSELF, AND DIDN’T TOUCH YOURSELF ONCE.” Black ran the end of the riding crop against Slim’s bulge, drawing out a moan and the tiniest shudder. “AND THE MALICIOUS AND HONORABLE SANS IS A MONSTER WHO KEEPS HIS WORD. HOWEVER…” He lifted the crop, and Slim’s hips twitched upward, bereft. “YOUR PUNISHMENT IS NOT OVER, BITCH. I’M STILL NOT CONVINCED YOU’VE LEARNED TO CONTROL YOURSELF.”

Black knelt down to sit astride on Slim’s legs just below his knees. His feet were tucked behind him. The position and the crop in his hands made him look like he was about to ride a horse, and with the bit in his mouth Slim almost fit the bill. “WHEN WE’RE DONE HERE TODAY, YOU’RE GOING TO REMEMBER WHOSE BITCH YOU ARE.”

“yorsh, m’lrd!” Slim croaked, realizing too late he’d interrupted his master.

The crop swung.

He winced.

But it didn’t strike. Just before the crop struck Slim’s ilium, it halted abruptly and became a gentle caress. Slim moaned softly, only just biting back another interruption meant to thank his master.

“I APPRECIATE YOUR EAGERNESS TO PLEASE,” Black murmured through clenched teeth. “BUT SPEAKING OUT OF TURN WILL _NOT_ MAKE THIS EASIER FOR YOU, MUTT.” Slim whimpered and nodded.

“AS I WAS SAYING,” Black continued, grabbing the ropes binding Slim’s femurs with his free hand. “YOU’RE GOING TO REMEMBER WHOSE BITCH YOU ARE. YOU DON’T CUM UNTIL I SAY. I DON’T CARE IF YOUR COCK IS ABOUT TO EXPLODE, YOU _WILL. NOT. CUM._ ” With each of the last three words, Black harshly thrust his hips against Slim’s knees, earning a delicious moan from the taller skeleton. Slim realized what was going to happen and he shuddered. This was going to be a very, _very_ difficult heat.

Using the ropes around his femurs as set of tight reins, Black began shamelessly grinding against Slim’s legs. Friction just below his knees should have meant nothing to Slim, but the sound of silk panties scraping against denim pants mixed with his brother’s soft grunts of effort only made his cock throb harder. He whimpered, pushing the back of his head into the pillow to gaze desperately up at the ceiling.

“EYES ON ME, BITCH,” Black snapped. Slim instantly complied, neck twinging from how fast he moved. “I WANT YOU TO WATCH THIS. REMEMBER, IF YOU’RE GOOD I’LL MAKE YOU THE HAPPIEST BITCH IN THE UNDERGROUND. WON’T THAT BE NICE?”

“ysh, m’lrd,” Slim whimpered.

“YES, IT WILL. NOW, BE A GOOD BITCH AND HOLD STILL…” Black picked up the pace, rutting against Slim’s knees as though if he did it hard enough, his cock would manifest down there to meet him. Slim shuddered, the ropes creaking with tension as he strained to not move. The motions his brother was making were _so_ close to making love, yet so, torturously far from being even remotely satisfying for him. Please, oh god, he needed...more...

Out of nowhere, Black lifted his full weight off of Slim’s legs and lunged forward, then ground his crotch against the middle of Slim’s femurs in a single, rolling stroke.

“AND NOW, THE REAL TEST OF YOUR LOYALTY, BITCH,” Black murmured. He grabbed the next nearest ropes in front of him to act as his reins again, which happened to be the ropes going around Slim’s pelvis.

“nnngk!” Slim squawked, unable to suppress a shudder which nearly set Black off balance, causing his master to pull on the ropes to stay in position.

“WHOA THERE, BITCH!” Black cackled, slapping the crop against pillow next to Slim’s shoulder, shocking the skeleton into stillness, forcing their eyes to meet. “I DIDN’T ASK FOR A RIDE. YOU ARE MY BITCH, _MY_ FUCKTOY! YOU DON’T RIDE ME UNLESS I ORDER YOU TO.” The rutting sped up again, Black’s new grip now close enough to Slim’s glowing bulge for every tug to pull his constricted package with merciless force.

“ysh...m’lrd…” Slim wheezed, saliva freely trailing down his jaw and onto the pillow.

Under the agony, he could feel warmth on his legs that couldn't have just been from the friction of his brother’s grinding. Gazing at his master, Slim couldn't help but notice a faint blue-purple glow starting to emanate from his pelvis despite his hazy vision. He whimpered nervously. No no _no_...if he caught a whiff of his master’s delicious mound in this state, it would all be over…

“HFF...HFF...WHAT’S THE MATTER, BITCH?” Black taunted. A purple flush had come over his face,  and his breath was labored from the vigorous, dry humping. “GETTING DISTRACTED?”

Slim made a keening sound, shaking his head from side to side. “n-nno, m’lrd!”

“NO?” Black gave a particularly hard thrust. “THEN YOU WON’T HAVE ANY TROUBLE IF I DO _THIS.”_ With a lustful growl, Black hoisted himself up and leapt forward again. His feet flew out in front of him, and his pelvis met Slim’s middle with such force that it knocked the wind from him with a terrified squawk. Instinctively he drew his knees up.

“DOING ALRIGHT DOWN THERE, BROTHER?” Black asked. His tone was light, but his eyes were diligently locked on his brother, watching his response carefully. Slim heaved in a few deep breaths, and once he had recovered a bit, tapped his feet together twice.

“GOOD.” Black inched his hips backward, pushing with his feet and pelvis until he had scooted himself directly on top of Slim’s bulge. Slim whined, rolling his hips needily. “WHAT DID I JUST SAY ABOUT YOU RIDING ME, BITCH?” Black tutted, waving the crop in front of Slim’s face threateningly.

“srrry, m’lrd,” Slim slurred, biting down hard on the bit in his effort to stay still. God, but he could feel his brother’s warm magic pulsing even through his jeans…

Black moved his hips in a slow circle, grinding directly against his brother’s throbbing, bound erection. It was then that Slim felt the metal studs sewn into the panties. The hard, blunt spikes made the grinding sound against his pants even louder, and provided a sharp, cold counterpoint to his master’s otherwise tantalizingly soft mound.

“hhhhggghhnnnn,” Slim moaned. “leese, m’lrd…”

“MMM?” Black hummed, grinding again just hard enough to shift his cock around, which was painfully erect and desperate to be unsheathed. “PLEASE WHAT? WHAT COULD A WORTHLESS BITCH LIKE YOU POSSIBLY ASK OF HER MASTER?”

“nnnn...leeese! leesh leh’ eee gum!” Slim cried, his tongue clumsily bobbing around the bit. Flecks of spittle flew out of his mouth, catching Black right in the face.

“TCH, SO MUCH DROOL,” Black scoffed, wiping his cheek in disgust. “YOU REALLY ARE A SLOPPY BITCH, AREN’T YOU? NO, I WILL NOT LET YOU CUM. THIS IS YOUR PUNISHMENT, REMEMBER?” He picked up the pace again, rocking ceaselessly against Slim’s luminescent bulge. “THIS IS WHAT YOU DID TO ME ALL. MORNING. LONG.” Black punctuated each word with an extra harsh thrust, his mouth curling into a sadistic grin.

“AND NOW IT’S MY TURN.”

Slim wasn’t sure how it was _possible_ to be so aroused without achieving satisfaction. He felt like a shaken up soda bottle that was about to burst. A visible stain of precum had appeared on his crotch, making the inside of his pants feel slick and dirty. His brother’s pussy had fully manifested behind the panties, the soft, warm mound separated from his ravenous cock by only a couple of layers of fabric. Demanding need burned through him in waves, each pulse of his SOUL powering the endless throbbing of his engorged cock. The cage of cloth created by his fly and the ropes around his pelvis created just enough pressure to be maddeningly tantalizing without allowing him any relief. His head fell back against the pillows and his tongue lolled out of his mouth from behind the bit, no longer able to form comprehensible words.

Black watched his brother writhe and moan beneath him with smug vindication. That’s right. Papyrus was _his_ bitch. His precious, loyal bitch. No matter what happened in town or on patrol, his brother was always at his side, always trusted and adored him. Even when he asked his brother to degrade himself, to go through _hours_ of consensual agony, he did it. With absolute certainty that Black would always do right by him, and never betray the sacred trust which had kept them together and alive all these years. And Black _would_ do right by his brother.

...Eventually. He had one more trial for his bitch before giving him his reward, and the needy throb in Black’s cunt signalled it was just about time to begin. He smirked, eye glowing dark purple as he ran his tongue over his pointed teeth hungrily. Yes, when he was done, his brother would be singing his praises for _months._

**Notes for the Chapter:**

> SO LIEK I'm a female, I have no idea what having a penis feels like lol. But from what I've read it's something like this? Something that desires friction, and to be put in something? And definitely something that doesn't like to be pushed down and caged (unless you're into that kind of thing, which Slim totally is). Hope I got a few things right anyway.
> 
> Oh, and Slim isn’t wearing underpants. Not sure how clear that was, but it will be in the next part~ I figured it wouldn’t really be a necessary thing for skeletons, since they don’t have any sensitive parts down there unless they’re aroused. So clothing for them is mostly for aesthetics. Black wears the panties just to be a tease, and because he knows he looks damn good in them.
> 
> Stop by tomorrow for the finale of this cocktease! I promise plenty of hot action <3 Because tomorrow’s kink is face sitting, plus a LOT more besides~


	3. Fuckin' Bitch

**Summary for the Chapter:**

> And now, the GRAND FINALE! Today is day 9, which like I said before had technically been swapped with day 8’s prompts. This configuration simply worked so much better, as you’re about to find out. Today’s prompts were latex, roleplay, and deep-throating/face sitting. I went with face-sitting, but then it exploded into...this. I guess you could say Black and Slim’s dom/sub dynamic is SORT OF role-playing, but since their roles are basically “dom and sub” I didn’t feel it was distinct enough to tag it as such.

“YOU’RE HAVE PLEASED ME WELL, MUTT. ARE YOU READY TO EARN YOUR REWARD?”

Slim blinked his eye sockets slowly, trying to pull his mind out of its heat-induced haze to comprehend what his brother had just said. He didn’t really want to though--returning to reality meant suffering through the unforgiving throb in his pants.

“hhhgghh…” he groaned, bringing his tongue back inside his mouth to try and form words around the gag. “yesssh, m’lrd…”

“EXCELLENT.” Black ceased his pitiless rutting and brought his knees beneath himself again, scooting up until he straddled Slim’s rib cage. His master filled Slim’s view, and for a moment he forgot all his worries and simply sat in awe of the vision before him. The spikes and cascading chains adorning his corset glittered softly in the dim light of the bedroom. A vibrant blue-purple glow emanated from behind his fine lace panties, which had ridden up to bunch along the cleft of his vulva and press the swollen folds apart. Slim could see his master’s arousal seeping through the cloth, could _smell_ his sweet pussy begging to be filled with the only cock which could satisfy it.

Not that his master showed any sexual desire outwardly. The way heunclipped the garter straps from his panties was so casual, he might have been unpinning clothes from a clothesline. But the soft, suggestive clicks still seemed to echo endlessly in the tensely silent room, making Slim shiver and swallow awkwardly as drool began to drip down his chin. After what might as well have been an eternity of teasing, the straps fell aside, and Black hooked a thumb beneath the waistband of the panties, savoring his control over the moment just a little longer.

“ARE YOU HUNGRY, BITCH?” Black whispered softly.

“mmmhmph,” Slim hummed, sucking in the drool that had begun seeping around the bit, then swallowing loudly. “yssh, m’lrd,” he amended when he saw his master’s dark look.

“I’M GLAD,” Black continued, pulling down the panties until his luminescent pussy came into view. The indigo light bounced off Black’s face and the corset’s spikes and chains, giving him a haunting, other-worldly appearance. “BECAUSE YOU’RE GOING TO EAT MY PUSSY UNTIL I CUM _THREE_ TIMES. ONLY THEN WILL I EVEN _CONSIDER_ LETTING YOUR WHORE COCK TOUCH ME. UNDERSTAND, BITCH?”

Slim let out a small whine. Of course his master would ask to cum first, that’s how it always went, even at the peak of his heat cycle. His brother had never failed to bring him satisfaction after putting him through something painful or strenuous. He trusted Sans would not start now.

“aih u-unnershan, m-m’lrd,” he agreed.

“GOOD.” Black leaned forward and gestured for Slim to lift his head up. He did, and Black reached behind his skull to unbuckle the gag, pausing briefly to be sure Slim had opened his mouth wide enough before pulling it out. Slim opened and closed his jaw a few times before speaking.

“thank you, m’lord,” he said, then twisted his tongue around this way and that to stretch out the soreness.

Black sneered. “DON’T THANK ME JUST YET, BITCH.” He then fully stood up on the bed, his booted feet still straddling Slim as he leisurely removed the panties from around his legs. He tossed the dainty garment on one of the bed posts, letting it hang lewdly from the wooden knob as a marker of his conquest.

Black then took a step forward, positioning his feet on either side of Slim’s head, taking a few seconds to make sure he was properly aligned. Slowly he went down to his knees, kneeling directly above Slim’s face. He lowered himself the last few inches very gently, until his pussy lips made contact with his dog’s mouth, parting just slightly as they connected.

Slim nearly opened his mouth the moment he felt the warm, wet magic-charged folds touch his teeth. But the sight of his master towering above him, alluring and formidable, gave him pause. Black’s pussy radiated heat onto his face, filling his senses with the warm, rich scent of musk, and the excited silent pulse from a SOUL that wasn’t his.

“AT LEAST YOU REMEMBERED ONE RULE, BITCH,” Black grumbled, not wanting to give his dog too much praise too early. “NOW, WHAT IS IT THAT YOU WANT TO DO?”

“please, m’lord, may i eat out your pussy?” Slim replied instantly.

“YES BITCH, YOU MAY.”

It took every bit of of Slim’s will and self-control to not thrust his lengthy, blood-orange tongue as far into his master’s folds as he could. Instead, he parted his jaw and ran the tip of his tongue up the length of the slit, earning an unexpected and sumptuous moan from his brother. Slim chuckled softly.

The flush on Black’s cheeks deepened. “DO YOU WANT ME TO MAKE IT FIVE TIMES, YOU CHEEKY BITCH?” he snapped.

“no m’lord,” Slim simpered, unable to hide the amusement in his voice. “my apologies, m’lord.”

Black crossed his arms with a huff and adjusted his position slightly. “WELL, GET ON WITH IT THEN.”

“gladly, m’lord.”

Slim’s tongue dipped shallowly into Black’s pussy, making a few basic circles to orient himself and make sure his brother was properly prepared. He brought his tongue back in his mouth, savoring the tang of Black’s juices for a moment before diving back in for more. He worked with purpose, starting with slow, shallow licks before working his way deeper with quick, burrowing thrusts.

Black allowed himself a small sigh of satisfaction as his brother eagerly got to work. It never ceased to amaze Black how _long_ his brother’s tongue was. Once when Slim had been particularly drunk at Muffet’s, he’d managed to stick it all the way up into an eye socket, and then poke it back out the other. So long…just like him. And like...other parts of him.

Thoughts about his brother were interrupted by several quick, forceful flicks against his clitoris. “NNGHK!” Black tensed up and his eyes widened, cumming a lot sooner than he had expected. It couldn’t have been more than a few minutes since Slim had started. Had he really been _that_ aroused? The scent of brother’s heat must have really gotten to him.

Slim’s sharp teeth brushed Black’s outer folds as he brought his mouth close to drink his brother’s cum, making rude slurping noises as he did so.

“one, m’lord!” he called. He swallowed loudly and moved on to the next course before Black could even catch his breath.

With a single thrust of his tongue Slim drove even deeper than he had before, this time twisting and wiggling it around for a few seconds before pulling back out to attend the labia, lightly brushing the clitoris just enough to cause Black’s hips to twitch involuntarily. Slim would have smiled if his mouth hadn’t been so busy. He knew _exactly_ how to work his brother up. He could map every inch of his brother’s pussy from memory alone, knew every fold, every crevasse. He knew each and every one of Black’s weaknesses, and was exploiting all of them to bring him to completion at a blistering pace.

A gentle nip at his clitorous with Slim’s sharp teeth made Black come again with a breathless and undignified squeal. Slim happily drank the fresh deluge of his brother’s juices, triumphantly crying “two, m’lord!” as he licked up the excess running down his chin.

Black scowled downward at his cheeky dog. He knew _exactly_ what his brother was doing, and briefly considered scolding him for insubordination. But aside from the fact that Slim wasn’t _technically_ breaking any rules—after all, he hadn’t specified how fast to make him cum—he wasn’t sure if he...if he could actually form the proper words to...to describe how he had been displeased.

After giving his teeth a final cleansing lick, Slim drove in again, giving Black the full length of his devilishly agile tongue.

“NAAAHHH...” Black moaned, his own tongue lolling out of his mouth as his brother twisted inside him in several corkscrews, somehow finding a way to flick the tip hard enough to hit his g-spot. Abandoning all pretense, Black began to thrust into his brother’s face, grinding down until his labia rubbed directly against Slim’s fangs with his hands on his brother’s chest for support.

Slim gratefully accepted the new angle, using the it to contort his tongue so that he both stimulated Black’s deep inner walls, and rubbed steady circles against his throbbing clitoris at the same time.

“HAAAAAAGH!” Black came with a scream. His claws raked Slim’s chest as his back arched and pussy clenched, entire body seizing up from ecstasy. Slim’s tongue froze, completely trapped by the walls of his brother’s cunt squeezing down around him like a vice. Before Slim could register the veritable goldmine of puns to be reaped from his tongue being caught in a pussy, hot, slippery fluid gushed into his mouth like a faucet had opened up above him. With his tongue trapped he couldn’t close his mouth or turn away, he _had_ to swallow every drop of release lest he choke—not that he would have _wanted_ to turn away. He gulped loudly and greedily, gasping for air between uneven swallows.

Black’s peak lasted half a minute before his cunt finally released and, the small skeleton went limp with a breathless sigh. His brother was not remiss in his duties however, sipping up the last few spurts of release that leaked out of him, then thoroughly cleaning Black’s pussy and all the surrounding areas he could reach, lapping up any and all stray splashes and droplets.

“GOOD, GOOD BOY, _FUCK,_ GOOD BITCH, OH YES…” Black chanted, eyes half closed in pure bliss. Fuck, Papyrus could clean up better than all the Woshuas in the Underground combined.

“thank you, m’lord,” Slim murmured, licking his teeth clean as he finished his task. “may i please cum now, m’lord?”

Black smirked, looking down at his brother’s hopeful, pleading eyes. He then giggled softly despite himself. So eager, and unbecoming of an obedient submissive to ask for his own reward. But he couldn’t deny his brother had certainly earned it, and then some. Now it was his turn to render his dog speechless with pleasure.

Black stood up slowly, then used the tip of the riding crop to tilt Slim’s chin up to face him. “YES, MY DARLING LITTLE BITCH, YOU HAVE SATISFIED ME. I DO BELIEVE YOU HAVE EARNED YOUR REWARD.” His mouth widened into a wicked grin.

Slim bounced eagerly in his bonds, unable to contain his excitement. “t-thank you, m’lord! thank you so, so much!”

Black stepped away from Slim knelt down beside him. He began pulling and testing each of the ropes around Slim by sliding two fingers behind each cord.“HOW ARE THE ROPES, IS ANYTHING SNAGGING? CAN YOU FEEL ALL OF YOUR BONES?” he asked attentively.

Slim wiggled his fingers and toes, rolled his shoulders experimentally, then nodded. “all is well, brother. green.”

Black finished testing every rope all the way down to his ankles, then nodded in return. “VERY GOOD.”

He got to his feet and was all business again. He tapped the riding crop threateningly in one hand, studying his submissive thoughtfully. “SO WHAT WAS IT EXACTLY THAT YOU WANTED ME TO DO TO YOU, BITCH?”

Slim shivered from the cool authority radiating from his master. “f-fuck me,” he whispered without thinking, then winced.

_Thwack!_

The crop struck just to the left of Slim’s bulge, causing the skeleton to cry out in pain and alarm. “TSK, TSK, TSK,” Black tutted. “YOU MAY BE GOOD AT GIVING HEAD, BUT YOU ARE ABYSMAL AT REMEMBERING YOUR MANNERS, UNGRATEFUL BITCH.”

The crop came down to the right of his crotch this time, and Slim yelped loudly, the stinging pain flowering out dangerously close to his throbbing, engorged cock.

“aaaaaagggh...i’m sorry, m’lord!” he pleaded. “please forgive me, i forgot my place!”

“DAMN RIGHT YOU DID, SNOTTY BITCH. YOU’RE LUCKY I DON’T JUST END THIS WHOLE THING RIGHT NOW.”

Slim shook his head wildly, struggling to lean up, instinctively trying to bow before his master. “n—please, m’lord, it was a mistake! please, i’ll be good, i’ll do anything, m’lord, anything! i...i’ll make you cum again! i’ll make you cum three more times—no, five!” he continued to flail, actual tears of frustration gathering in the corners of his eye sockets.

Before his brother could panic any more, Black pressed the end of the riding crop gently on his mouth, silencing his protests. “I AM DISPLEASED THAT YOU ADDRESSED ME IN SUCH A WAY. AND BELIEVE ME YOU WILL PAY DEARLY FOR THE SLIP, WHELP.” Slim whimpered, but said nothing. “FOR NOW, THOUGH...I WILL TEMPORARILY OVERLOOK THIS TRANSGRESSION. IF FOR NO OTHER REASON THAN TO GET YOUR REWARD OVER WITH AS SOON AS POSSIBLE SO I CAN PLAN YOUR PUNISHMENT.”

Slim perked up at this. “...r...really…? t-thank you, thank you m’lord!”

Black rolled his eyes and stepped back over Slim, brandishing the crop threateningly as he stood directly over his brother’s crotch. “YES, YES. NOW, TELL ME WHAT YOU WANT, BITCH— _PROPERLY_ THIS TIME.”

The bound skeleton shamelessly bucked his hips up and down on the mattress, as though he’d be able to meet his brother’s pussy if he bounced high enough. “you, m’lord! I want you to fuck me, please, m’lord!”

“FUCK YOUR _WHAT?_ I’VE ALREADY FUCKED YOUR FACE, YOU SPOILED BITCH. SO YOU’RE GOING TO HAVE TO BE MORE SPECIFIC THAN THAT...”

 _“_ my cock! _please_ fuck my cock, m’lord!” Slim begged. “take me, use me as your fucktoy, take what is yours m’lord!”

Black’s face split into a toothy grin. He slowly bent down, then ran a single, gloved finger across Slim’s warm, pulsing mound. The bound skeleton whined, then shuddered as Black did it again, harder. “VERY WELL. SINCE IT IS ALREADY MINE,” Black growled softly. He unbuttoned the top of his dog’s jeans, then took the zipper toggle between two fingers with a coy smile. Slim nodded pleadingly, and Black slowly began to unzip him. The little mechanism moved surprisingly smoothly, the teeth making the smallest sound as something large and bright began to shift beneath the fabric. Slim gasped in relief and his cock sprang out, immediately standing fully erect. It curved slightly back, its considerable length the vivid hue of a blood orange glowing brightly enough to throw shadows onto the bed sheets.

It was Black’s turn to salivate. He didn’t usually lower himself to give head, but in this moment he might have considered it. Several beads of precum slid down the shaft, orange and red swirls of competed for dominance under the translucent, magical membrane of his brother’s cock. Colors and waves of magic pulsed in time with the rhythm of Slim’s SOUL, which Black felt calling out to him longingly.

He could no longer deny himself. Black dropped to his knees and put his hands on Slim’s chest, lifting his ass into the air as he lined himself up, then pressed down.

Slim took a sharp breath as Black’s folds swallowed up his tip, whining like a sad dog when Black paused with barely an inch of him inside. _LIKE A BITCH,_ Black thought wickedly.

“please, _please,_ m’lord...i’m begging you, please take me, _please_ fuck me…” Slim quietly babbled, hands twisting in his bonds as he fought with all his might to not thrust upward and finish the job himself.

“MWA HA HA HA~” Black chuckled darkly. “HERE COMES YOUR TREAT, BITCH. YOU’D BETTER ENJOY IT~” He lowered himself the rest of the way, sliding frictionlessly down the length of Slim’s shaft, letting out a small moan as the sizable girth stretched his inner walls almost enough to be painful. _Almost._

“ooooouuuughhh,” Slim trembled, unable to stop his hips from rolling forward. This earned a slap of the riding crop on the pillow just beside Slim’s face, close enough that he felt the air displaced by it.

“WHO IS RIDING YOUR COCK, BITCH?” Black questioned dangerously.

“you are riding my cock, m’lord. only you, alwa—aaaagh!”

As Slim answered, Black sat back up, until just the tip of the head barely remained in his pussy. “oh please m’lord, _please…”_

Black seated himself again, and another salacious moan passed from Slim’s mouth. He did this several times, pulling himself almost completely off of Slim’s shaft, then completely hilting himself again.

“ARE YOU HAPPY, YOU SLUTTY BITCH? I’M FUCKING YOUR COCK. THIS IS EXACTLY WHAT YOU ASKED FOR.”

“oh fu—yes, m’lord, thank you. but, please, m’lord…”

 _“PLEASE?_ PLEASE WHAT? IF YOU WANT SOMETHING THEN ASK FOR IT, YOU NEEDY BITCH.”

Black punctuated his sentence by sheathing himself again, and Slim’s cock twitched urgently. “nnnngh, please m’lord, more! faster, please!”

“OH, FASTER? YOU MEAN LIKE THIS?” Black leaned forward and rolled his hips, not pulling out as far and moving just marginally faster.

“yes, m’lord, yes! just like that, oh stars…”

Black pulled out to the tip again and paused. “WELL TOO FUCKING BAD. BITCHES DON’T GET TO CHOOSE HOW THEY’RE FUCKED. THEY’RE FUCKED HOW THEIR MASTERS SEE _FIT.”_

“nnn...oh, m’l-lord _please…”_

Frankly, it was taking all of his Black’s willpower to not fuck his brother senseless right here and now. The scent of Slim’s heat and the maddening pulse of his cock had Black well on his way to a fourth orgasm. But the one thing that made fucking his brother all the sweeter was getting him to _scream_ for it, and he was not going to throw away all the work he had done to get here.

After a few more minutes of torturously slow fucking that had Slim on the verge of tears, Black picked up the pace, leaning forward again to make shallow but quick thrusts. The new angle hit Black’s inner walls perfectly, drawing out a sigh of relief from both skeletons.

“aaah...thank you, m’lord. thank you!” Slim cried. “y-you are magnificent, you are just! nnnnaaaaaaghh…” He swallowed, panting uncontrollably. “i belong to you alone, m’lord! my cock belongs to you!”

Black almost laughed. He knew what Slim was after, can’t couldn’t fault him for his enthusiasm even if his attempt at manipulation was pathetically transparent. “THAT’S RIGHT, SING MY PRAISES BITCH. WHO’S FUCKING YOU RIGHT NOW?”

“you are, m’lord! you are fucking my cock!”

“GOOD ANSWER,” Black purred, leaning forward even further so that he was almost lying on Slim’s chest, taking the cock even faster. “WHOSE BITCH ARE YOU?”

“i am your bitch, m’lord!” Black felt Slim’s cock twitch inside him. “ooh, oooooh...please, m’lord may i cum?!” Slim pleaded urgently.

“JUST A LITTLE LONGER, BITCH. DO YOU LIKE ME FUCKING YOUR COCK WITH MY PUSSY?”

“oh yes, m’lord i love you fucking my cock with your pussy, aaagh!” Slim writhed as another urgent pulse struck his cock. He wasn’t going to be able to hold on much longer, even for his lord—his brother—this was just too much…

“YOU LIKE GETTING PUT IN YOUR PLACE, BITCH?” Black sped up even further, pounding Slim’s cock at a punishing pace.

“a-a-ha—yes! yes i love being put in my place! please put me in my place, m’lord!”

“YOU LIKE GETTING LAID OUT AND FUCKED LIKE THE BITCH YOU ARE?”

 _“yes,_ oh yes m’lord! I love getting laid out and—ah—fucked—nngh _—likethebitchiam!”_

“AND YOU WANT TO CUM, DON’T YOU BITCH?”

“oh, _fuck_ yes lord i want to cum...oooooh _please_ brother can i cum?!”

“CUM, BITCH!” Black ordered, slamming the crop down on the sheets to make a loud twack. “GIVE ME ALL YOUR CUM! HOLD NOTHING BACK!”

 _“aaaaaaaaaaaaaggghhh!”_ Slim screamed, squeezing his eyes shut as he lost all control. He slammed his hips up to meet his brother’s, forcing Black to straighten then arch his back to keep balanced. He continued to scream as fountains of cum erupted from his cock, shooting far up into Black, causing the smaller brother to freeze as the hot release not only filled his pussy, but spurt up into his ribcage and on his SOUL. Black gasped, completely unprepared for the orgasm that took him as his SOUL flared with magic, reacting to his brother’s ejaculate.

The piercing light shining from Black’s SOUL was completely lost on Slim, who was still mindlessly pumping his hips as he came long and hard. Relief had turned to desperation. Slim was unsure how long he could keep cumming like this, but also unsure if he could _stop_. Each hot stream came with a burning tingle shooting through his cock that was so intense it should have hurt, but he never wanted it to stop, never wanted to give up this feeling of complete satisfaction and release. It was as though his cock was no longer his.

That was right though, his cock _wasn’t_ his, it was his brother’s. His brother whose pussy was clamped down on him, milking him for everything he had, refusing to let him come down from this climax until he had taken all. Yes, Slim could keep going, he would give his brother all of his cum—no, his very _SOUL_ if that’s what he wished. His sweet, generous, magnificent brother deserved nothing less.

After what might have been days or weeks to Slim’s senseless mind, Black’s walls released his cock and the smaller skeleton went limp on top of him. Not long after that Slim came down from his climax, sweating and shaking all over, his cock still shuddering as it reluctantly surrendered the high. He tingled all over, his bones were soft and sensitive, once again sensing the resistance of every rope and knot holding him comfortably captive on the bed.

His sockets felt heavy, and he had trouble manifesting his eye lights to gaze upon his brother. “than...thank you m’lord…” he mumbled, surrendering to the contented drowsiness falling over him. “y-you are...so good brother...so good...thank you...thank you so…”

_Thwack!_

The riding crop struck the pillow just beside Slim’s face and he jolted to awareness. Black was kneeling next to him on the bed, apparently he had dismounted while Slim had been too far gone to notice.

“THAT WAS VERY GOOD, BITCH,” he whispered sinisterly. “YOU HAVE MADE ME _VERY_ HAPPY. BUT I DO BELIEVE I SAID AT THE BEGINNING THAT YOU AREN’T FINISHED UNTIL _I_ SAY SO.”

He pulled off one of his long gloves and reached over to Slim’s cock, which was half-masted and coated from tip to base in purple and orange ejaculate. With a cold smile, he wrapped his fingers firmly around the base.

“nnnghaaaaa...m-m’lord?!” Slim choked. His member was extremely overstimulated and sensitive, and the grip of his brother’s bony hand was mercilessly tight.

“I TOLD YOU I’D FUCK THIS HEAT RIGHT OUT OF YOU, AND THAT IS PRECISELY WHAT I MEAN TO DO. ONLY THE _BEST_ FOR MY BITCH.” Black gave him single hard stroke. It made an obscene squelching sound, and Slim squirmed hard in the bindings, partly amazed he could still feel anything at all, and partly afraid of what exactly his brother had planned for him. “I’M GOING TO WRING EVERY LAST DROP OF CUM OUT OF YOUR FILTHY COCK. YOU’LL SPILL SO MUCH MAGIC ONTO THESE SHEETS YOU WON’T BE ABLE TO MANIFEST THIS THING FOR A MONTH.”

Black began jerking him off in quick, pitiless strokes and Slim moaned in tormented pleasure. He was bound up and in the best kind of agony, and he wouldn’t have stopped it for every star in the heavens. Everything he had gone through before was paying off, and he would accept his brother’s gift gratefully, even if it left him helplessly cumming all over himself for hours on end and he passed out from sheer bliss.

.

“but m’lord, at least let me help with the sheets…”

“FOR THE LAST TIME _NO,_ MUTT. YOU SIT IN THAT TUB AND DRINK YOUR TEA. I’LL TAKE CARE OF THE BLEEDING LAUNDRY.”

Slim sighed forlornly as his brother left the bathroom, sipping the mixture of chamomile and lavender from his dainty cup. He was up to his ribcage in luxurious bubbles, with the knees of his awkwardly long legs sticking out just above the surface. He was physically and mentally exhausted, yet he still had to fight the urge to step out of the bathtub and help his brother with the cleanup. Black was just as strict with his aftercare as he was with his BDSM, if not more so. As much as it bothered Slim to not help with the household chores, it was rather amusing to watch the small form of his brother wrangle sheets that were several times larger than himself.

Black returned after some minutes, untying and shimmying out of his corset. Slim noted the vivid red-orange stains all over his brother’s ribcage, and especially on the inside. He opened his mouth to ask a question, and then it dawned on him. He blushed and took another sip, unable to hide his smirk.

“YES, YES,” Black muttered, knowing exactly what Slim had seen. “THE DISCOLORATION MAY NEVER COMPLETELY WASH OUT. I HOPE YOU’RE SATISFIED, MUTT.”

“very much so, m’lord,” Slim responded. “i guess you could say it means i’ll always be with you.”

Black started, glancing at his brother then down at the floor as a blush creeped onto his face. “AHEM, YES...I SUPPOSE THAT IS ONE WAY OF LOOKING AT IT.” He rushed over to the far wall, rinsing himself down with a moveable shower head mounted over a drain before joining Slim in the tub. He situated himself opposite to his brother, leaning his back against the other side of the tub with a small sigh.

“HOW ARE YOU FEELING? DOES YOUR PELVIS ACHE? DID ANYTHING CHAFE? DO YOU NEED BURN OINTMENT?”

Slim waved a hand at the bombardment of questions. “i’m fine, brother, really. i am a bit sore, but that’s to be expected.”

“YES...BUT WHAT ABOUT—”

Slim lifted a foot out of the tub and pressed his toes against Black’s mouth to silence him. _“brother._ be still. i will tell you if something is amiss. you know i will.”

Black blinked a few times, then gently shoved the foot away. “ALRIGHT, ALRIGHT. YES I _KNOW._ STILL—”

“and what about you, brother? would you like some tea? you worked hard today, too.”

The smaller skeleton grumbled a moment, before conceding that yes he did want some tea. They sat in contented silence for some time, enjoying their tea and each other’s company.

When Slim finished his second cup, he set it aside and cleared his figurative throat. “brother…?”

“YES?”

Slim shifted uncomfortably. “next time...instead of the crop, could we try something else?”

His brother leaned forward in concern. “OF COURSE, BROTHER. WAS THE CROP TOO MUCH? I COULD—”

“like a switch.”

Black peered at him. “A SWITCH? THAT WILL HURT MORE THAN THE CROP. ARE YOU CERTAIN?”

“yes, i think so. i’d at least like to try it. after all, you know what they say…”

Slim got the last part of his statement out just before his brother’s indignant splash hit him in the face.

“bitches get switches.”

**Notes for the Chapter:**

> Okay, so I realize this got way out of hand and goes way above and beyond the original prompt. But I figured after two chapters of literal cockteasing, it was time for some serious payoff, haha. Plus it didn’t feel right to not show Slim’s reward after all that punishment. Healthy BDSM relationships are all about fair exchanges of power and pleasure. Black is a tough dom, but he’s always fair, and he always makes sure the reward is well worth what he puts his sub through.
> 
> And he knows when to loosen up, too. For example, normally he wouldn’t allow Slim to break out of calling him “m’lord” during a scene or let him thrust without permission. But he was willing to let it slide there at the end considering how much he had done to make that moment of release so intense. At that point the most important thing to him was seeing to Slim’s pleasure, and while punishing him for that would have been in-character, it would have put a damper on Slim’s moment.
> 
> Tomorrow I’ll be taking a short break, since it’s day 10 which was supposed to be the fucking machine prompt, buuuut as some of you may know, I already released that fic and it’s follow-up in advance of kinktober. It’s called “Underswap Alphyne Sexploits” if you haven’t seen it already, and was the first story I posted on this account.
> 
> So the next story will come out Wednesday, and will feature the kinks S&M, orgasm denial, AND gags! I KNOW I’ve already covered those kinks in the other stories several times over now (including this one), but those three are like in my top 5 kinks of ALL TIME so fuck it they’re getting their own story. In case you’re wondering, the other two would be bondage and non-con/rape fantasy. BIG SURPRISE I KNOW.

**Author's Note:**

> Swapfell is one AU I’ve never put a lot of thought into. But for some reason when it came to dirty talk, Swapfell Sans was the one that stood out in my mind. I’ve got no clue if I did this dirty talk thing right. I enjoy reading it but I don’t know the first clue about writing it (or saying it out loud jfc). All I knew was I wanted something degrading to lead into the next parts of this. That’s right, not one but TWO future fics this month shall continue this saga! Will Slim be a good boy and not touch himself? Or will he be bad, and need to be punished? Find out next time~
> 
> And a HUGE thanks to Ravvi for betaing all three chapters of this story and helping dial the hotness up to 11.
> 
> https://ravvi-k.tumblr.com/
> 
> Tomorrow's kink will be biting. And don't worry, it is a little longer than this one.


End file.
